JP6115189B2 - Quantum entangled photon pair generator - Google Patents

Description

  The present invention relates to a entangled photon pair generating device that generates a entangled photon pair.

  An entangled photon pair generating device that generates entangled photon pairs is an important component for realizing quantum information communication technology such as quantum cryptography and quantum computers. Various technologies have been studied for the purpose of realizing a entangled photon pair generator. Among various techniques, a technique using parametric fluorescence in a nonlinear optical medium is most practical.

  Parametric fluorescence is a nonlinear optical phenomenon in which a pair of photons called signal photons and idler photons are generated when one or more excitation photons are input to a nonlinear optical medium. Here, the excitation photon, the signal photon, and the idler photon have a correlation corresponding to an energy conservation law or a correlation with respect to polarization.

By utilizing these correlations, a entangled photon pair can be generated. For example, Non-Patent Document 1 discloses a quantum entangled photon pair generating device that generates a polarization entangled photon pair having a polarization correlation between a photon pair of a signal photon and an idler photon. Here, as a nonlinear optical medium, a Sagnac interferometer type optical interferometer using a LiNbO ₃ crystal (PPLN crystal) with a periodic modulation structure is formed, thereby forming a polarization entangled photon Generating a pair.

H. C. Lim, A.A. Yoshizawa, H .; Tsuchida and K.K. Kikuchi, “Stable source of high quality telecom-band polarization-entangled photo-pairs based on a single, pulse-pumped, short PPLNwp. Vol. 16, no. 17, pp. 12460-12468 (2008)

  When generating a entangled photon pair using parametric fluorescence, a light source of excitation photons is necessary to generate the parametric fluorescence phenomenon. For example, in the entangled photon pair generation device disclosed in Non-Patent Document 1, the light source of excitation photons (hereinafter referred to as excitation light source) is an optical that generates a entangled pair such as an optical interferometer including a nonlinear optical medium. It is prepared separately from the system.

  For this reason, the quantum entangled photon pair generating device having the excitation light source and the optical interferometer is large and expensive as a whole.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a more compact and low-cost quantum entangled photon pair generating apparatus in which an excitation light source and an optical interferometer are integrated. There is.

  In order to achieve the above-described object, a quantum entangled photon pair generating apparatus of the present invention includes a laser resonator, a polarization plane converter, a polarization beam splitter, and a WDM (Wavelength Division Multiplexer / Demultiplexer) filter. Is done. The laser resonator has an optical gain in a frequency band including the optical frequency ωp, and generates an excitation photon with the optical frequency ωp. Due to the nonlinear optical effect, a signal photon with the optical frequency ωs and an optical frequency ωi with the optical frequency ωi are generated. A non-linear optical medium that generates a photon pair of idler photons, and first and second photon pair extraction units that are provided at positions sandwiching the non-linear optical medium in the propagation direction of excitation photons and that extract signal photons and idler photons. Yes. The polarization plane converter rotates the polarization directions of the signal photon and idler photon extracted from the first photon pair extraction unit by 90 degrees. The polarization beam splitter combines the output light from the polarization plane converter with the output light from the second photon pair extraction unit. The WDM filter spatially separates the output light from the polarization beam splitter into the wavelength component of the signal photon and the wavelength component of the idler photon.

  According to the entangled photon pair generating apparatus of the present invention, the nonlinear optical medium is provided inside the laser resonator. That is, a light source of excitation photons (hereinafter referred to as an excitation light source) and an optical system that generates a entangled pair such as an optical interferometer including a nonlinear optical medium are integrated. For this reason, the quantum entangled photon pair generating device can be made smaller and lower in cost.

It is a schematic block diagram of a 1st entangled photon pair generator. It is a schematic diagram which shows the characteristic of the wavelength separation filter used for the 1st entangled photon pair generator. It is a schematic diagram which shows the characteristic of the optical band pass filter used for the 1st entangled photon pair generator. It is a schematic block diagram of the 1st modification of a 1st entangled photon pair generator. It is a schematic block diagram of the 2nd modification of a 1st entangled photon pair generator. It is a schematic block diagram of the 2nd entangled photon pair generator. It is a schematic diagram which shows the characteristic of the wavelength separation filter used for the 2nd entangled photon pair generator. It is a schematic block diagram of the modification of a 2nd entangled photon pair generator. It is a schematic block diagram of a laser resonator.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the shape, size, and arrangement relationship of each component are merely schematically shown to the extent that the present invention can be understood. In the following, a preferred configuration example of the present invention will be described. However, the material and numerical conditions of each component are merely preferred examples. Therefore, the present invention is not limited to the following embodiments, and many changes or modifications that can achieve the effects of the present invention can be made without departing from the scope of the configuration of the present invention.

(First entangled photon pair generator)
With reference to FIG. 1, a first embodiment of a entangled photon pair generation device (hereinafter also referred to as a first entangled photon pair generation device) according to the present invention will be described. FIG. 1 is a schematic configuration diagram of a first entangled photon pair generating device.

  The first entangled photon pair generating apparatus 10 includes a laser resonator 20 and a photon pair output unit 80.

  The laser resonator 20 includes an optical amplifier 30, a nonlinear optical medium 40, first and second photon pair extraction units, a narrow band optical bandpass filter 64, and an optical delay circuit 66, and is a loop resonator. It is configured as. The laser resonator 20 oscillates at the optical frequency ωp. The photon pair output unit 80 includes a polarization plane converter 82, a polarization beam splitter 84, an optical low-pass filter 86, and a WDM (Wavelength Division Multiplexer / Demultiplexer) filter 88.

  One end face 30 a of the optical amplifier 30 is optically coupled to one end face 40 a of the nonlinear optical medium 40 by the first optical path 60. The other end face 30 b of the optical amplifier 30 is optically coupled to the other end face 40 b of the nonlinear optical medium 40 by the second optical path 61.

  The first optical path 60 is provided with a narrow-band optical bandpass filter 64 and a first wavelength separation filter 50 as a first photon pair extraction unit. The first wavelength separation filter 50 includes first to third input / output ends 50a to 50c. The first input / output end 50 a of the first wavelength separation filter 50 is connected to one end face 40 a of the nonlinear optical medium 40. The second input / output end 50 b of the first wavelength separation filter 50 is connected to one end face 30 a of the optical amplifier 30 via a narrow band optical bandpass filter 64. The third input / output terminal 50 c of the first wavelength separation filter 50 is connected to the polarization plane converter 82 of the photon pair output unit 80.

  The second optical path 61 is provided with a second wavelength separation filter 51 as an optical delay circuit 66 and a second photon pair extraction unit. The second wavelength separation filter 51 includes first to third input / output ends 51a to 51c. The first input / output end 51 a of the second wavelength separation filter 51 is connected to the other end face 40 b of the nonlinear optical medium 40. The second input / output end 51 b of the second wavelength separation filter 51 is connected to the other end face 30 b of the optical amplifier 30 via the optical delay circuit 66. The third input / output end 51 c of the second wavelength separation filter 51 is connected to the polarization beam splitter 84 of the photon pair output unit 80.

  The polarization beam splitter 84 includes first to third input / output ends 84a to 84c. The first input / output end 84 a of the polarization beam splitter 84 is connected to the third input / output end 51 c of the second wavelength separation filter 51. The second input / output end 84 b of the polarization beam splitter 84 is connected to the third input / output end 50 c of the first wavelength separation filter 50 via the polarization plane converter 82. The third input / output end 84 c of the polarization beam splitter 84 is connected to the WDM filter 88 via the optical low-pass filter 86.

  The optical amplifier 30 has an optical gain in a frequency band near the optical frequency ωp including the optical frequency ωp, and generates pumping photons having the optical frequency ωp. As the optical amplifier 30, any suitable known optical amplifier such as a semiconductor optical amplifier or an optical waveguide type amplifier such as an erbium-doped optical fiber waveguide can be used. Here, an example in which a semiconductor optical amplifier is used as the optical amplifier 30 will be described. In this case, a drive power supply 34 is provided for generating an optical gain by injecting current into the optical amplifier 30. When the optical amplifier is an optical waveguide type amplifier, a light source that generates excitation photons may be used instead of the drive power supply 34.

  Further, it is desirable that both end faces 30a and 30b of the optical amplifier 30 are coated with antireflection to avoid operational instability due to reflected return light.

  Here, it is assumed that the oscillation polarization direction of laser oscillation is V-polarized light. This laser oscillation light propagates through the laser resonator in both the clockwise and counterclockwise directions.

The nonlinear optical medium 40 generates a photon pair of a signal photon having an optical frequency ωs and an idler photon having an optical frequency ωi from an excitation photon by a nonlinear optical effect. As the nonlinear optical medium 40, for example, a LiNbO ₃ crystal (PPLN crystal) with a periodically modulated structure can be used. Here, the d33 component of LiNbO ₃ crystal is used. When the lasing polarization direction of laser oscillation is V polarization, the LiNbO ₃ crystal is arranged so that the c-axis direction matches the V polarization direction.

  In this example, the period of periodic polarization inversion is set in the nonlinear optical medium 40 so as to cause natural parametric down conversion as a nonlinear optical effect. The nonlinear optical medium generates a signal photon and an idler photon as natural parametric down-converted light for the excitation photon. At this time, the optical frequencies ωp, ωs, and ωi of the excitation photons, signal photons, and idler photons satisfy the relational expression ωp = ωs + ωi. Further, the optical wavelengths λp, λs, and λi of the excitation photon, signal photon, and idler photon satisfy the relational expression 1 / λp = 1 / λs + 1 / λi. When a 1.5 μm band is desired as the wavelength band of the entangled photon pair, 0.75 μm may be used as the wavelength band of the excitation photon.

  Further, it is desirable that both end faces 40a and 40b of the nonlinear optical medium 40 are coated with antireflection to avoid operational instability due to reflected return light.

  The first and second wavelength separation filters 50 and 51 are provided at positions where the nonlinear optical medium 40 is sandwiched in the propagation direction of the excitation photons. The first and second wavelength separation filters 50 and 51 extract signal photons and idler photons from the laser resonator 20. Further, the first and second wavelength separation filters 50 and 51 propagate the excitation photons having the optical frequency ωp into the laser resonator to cause laser oscillation.

  Therefore, the first and second wavelength separation filters 50 and 51 are low in frequency having a frequency less than the boundary frequency ωx between the optical frequency ωs of the signal photon and the optical frequency ωi of the idler photon and the optical frequency ωp of the excitation photon. It is preferable that the photons of the frequency component are taken out from the laser resonator 20 and the photons of the high frequency component having a frequency equal to or higher than the boundary frequency ωx are directly propagated in the laser resonator 20.

  The input / output characteristics of the wavelength separation filter will be described with reference to FIG. FIG. 2 is a schematic diagram showing input / output characteristics of the wavelength separation filter. In FIG. 2, the horizontal axis indicates the optical frequency, and the vertical axis indicates the transmittance in arbitrary units. In FIG. 2, the solid line I indicates the transmittance output from the second input / output terminal with respect to the light input to the first input / output terminal, and the dotted line II is input to the first input / output terminal. The transmittance output from the third input / output terminal with respect to the measured light is shown.

  The wavelength separation filter that constitutes the first and second photon pair extraction units and exhibits these characteristics can be realized using a commercially available optical high-pass filter or optical low-pass filter.

  The light output in the clockwise direction from one end face 40 a of the nonlinear optical medium 40 is input to the first input / output end 50 a of the first wavelength separation filter 50. Of the light input from the first input / output terminal 50a, a high frequency component having a frequency equal to or higher than the boundary frequency ωx is output from the second input / output terminal 50b and propagates clockwise through the loop resonator. On the other hand, a low frequency component having a frequency lower than the boundary frequency ωx is extracted from the third input / output terminal 50 c to the outside of the laser resonator 20. The low frequency component light extracted from the third input / output terminal 50 c is sent to the polarization plane converter 82 of the photon pair output unit 80.

  On the other hand, the light output from one end face 30a of the optical amplifier 30 and propagating counterclockwise is input to the first wavelength separation filter 50 from the second input / output end 50b. A high frequency component having a frequency equal to or higher than the boundary frequency ωx input from the second input / output end 50 b is output from the first input / output end 50 a and sent to the nonlinear optical medium 40.

  Further, the light output in the counterclockwise direction from the other end surface 40 b of the nonlinear optical medium 40 is input to the first input / output end 51 a of the second wavelength separation filter 51. Of the light input from the first input / output end 51a, a high-frequency component having a frequency equal to or higher than the boundary frequency ωx is output from the second input / output end 51b and propagates counterclockwise through the loop resonator. On the other hand, a low-frequency component having a frequency lower than the boundary frequency ωx is extracted from the third input / output terminal 51 c to the outside of the laser resonator 20. The low-frequency component light extracted from the third input / output terminal 51 c is sent to the polarization beam splitter 84 of the photon pair output unit 80.

  On the other hand, the light that is output from the other end face 30 b of the optical amplifier 30 and propagates clockwise is input to the second wavelength separation filter 51 from the second input / output end 51 b. A high frequency component having a frequency equal to or higher than the boundary frequency ωx input from the second input / output end 51 b is output from the first input / output end 51 a and sent to the nonlinear optical medium 40.

  Here, the laser resonator 20 is preferably provided with a narrow band optical bandpass filter 64.

  With reference to FIG. 3, the input / output characteristics of the narrow-band optical bandpass filter will be described. FIG. 3 is a schematic diagram showing input / output characteristics of a narrow-band optical bandpass filter. In FIG. 3, the horizontal axis indicates the optical frequency, and the vertical axis indicates the transmittance in arbitrary units.

  The narrow band optical bandpass filter 64 is used to limit the oscillation frequency of the laser resonator to the optical frequency ωp. This can suppress laser oscillation at an optical frequency where phase matching cannot be achieved, thereby increasing the generation efficiency of the entangled photon pair.

  Moreover, generation of photon pairs other than the combination satisfying the relational expression of ωp = ωs + ωi can be suppressed. That is, if the optical frequency of the excitation photon is limited to one, the optical frequency ωi of the idler photon corresponding to the optical frequency ωs of the signal photon is also limited to one. For this reason, the correlation degree of photon correlation can be raised.

  The laser resonator 20 is preferably provided with an optical delay circuit 66. The optical delay circuit 66 is used for adjusting the laser resonator length and adjusting the phase difference of pumping photons input to the nonlinear optical medium 40 from both the left and right directions. By adjusting the laser resonator length, the optical frequency of laser oscillation is adjusted to the optical frequency ωp of the excitation photon. In addition, the degree of entanglement can be maximized by adjusting the phase difference.

  As described above, in the first entangled photon pair generation device 10, the laser resonator 20 takes out the signal light and idler light propagating clockwise through the loop resonator from the first wavelength separation filter 50, and counterclockwise. The signal light and idler light propagating around are taken out from the second wavelength separation filter 51.

  The photon pair extracted from the first wavelength separation filter 50 is sent to the polarization beam splitter 84 via the polarization plane converter 82. The photon pair extracted from the second wavelength separation filter 51 is sent to the polarization beam splitter 84 as it is.

  The polarization plane converter 82 rotates the polarization directions of the signal photon and idler photon extracted from the first wavelength separation filter 50 by 90 degrees. Here, when the signal photon and the idler photon are V-polarized light, they are converted to H-polarized light by the polarization plane converter 82.

  As the polarization plane converter 82, for example, a polarization-maintaining optical fiber obtained by converting the 90 ° optical axis at an intermediate position and fusion-splicing can be used. Further, when the optical frequency ωs of the signal photon and the optical frequency ωi of the idler photon are close, a half-wave plate may be used.

  The polarization beam splitter 84 has first to third input / output ends 84a to 84c. The V-polarized linearly polarized light input from the first input end 84a is output from the third input end 84c. Further, the H-polarized linearly polarized light input from the second input end 84b is output from the third input end 84c. As described above, the polarization beam splitter 84 combines the V-polarized light and the H-polarized linearly polarized light into the polarized light and outputs it.

  The light output from the polarization beam splitter 84 is sent to the optical low-pass filter 86. The optical low-pass filter 86 transmits the signal photon and the idler photon, sends them to the WDM filter 88, and blocks the excitation photons.

  The light output from the optical low pass filter 86 is sent to the WDM filter 88. The WDM filter 88 spatially separates the wavelength component of the signal photon and the wavelength component of the idler photon, and outputs them as a polarization quantum entangled photon pair. The WDM filter can be configured by using, for example, an arrayed waveguide grating (AWG: Arrayed Waveguide Grating).

  In addition, the quantum entangled photon pair generator may use a collimator lens or the like to configure each component as a spatial optical system, or an optical fiber connected to each component commercially available as an optical module using an optical fiber connector or the like. You may comprise as an optical system. The optical system constituting the quantum entangled photon pair generating device is preferably a polarization maintaining optical system. However, if the optical module is not a polarization maintaining optical system, a polarization plane controller or the like may be inserted.

  According to the first entangled photon pair generating apparatus, the laser resonator as the excitation light source unit and the photon pair generating unit including the nonlinear optical medium are integrated. Therefore, it is possible to provide a entangled photon pair that is smaller and less expensive. In addition, since it is not necessary to extract the excitation light outside the laser resonator, the efficiency becomes higher.

(First modification of first entangled photon pair generating device)
A first modification of the first entangled photon pair generating device will be described with reference to FIG. FIG. 4 is a schematic diagram of the entangled photon pair generating device 11 of the first modification.

  In order to maximize the degree of entanglement, it is necessary to make the generation probabilities of V-polarized photon pairs and H-polarized photon pairs the same. For this purpose, it is preferable that the intensity of the excitation light input to the nonlinear optical medium is equal for both the first optical path 60 and the second optical path 61.

  Therefore, in the laser resonator 21 of this modification, the first and second optical amplifiers 31 and 32, the first and second optical amplifiers 31 and 32, and the first and second wavelengths are used. Separation filters 50 and 51 are arranged symmetrically about the nonlinear optical medium 40. With this configuration, the generation probabilities of the V-polarized photon pair and the H-polarized photon pair can be made the same. Further, when the loss characteristics of the first and second wavelength separation filters 50 and 51 vary, the optical gains of the two optical amplifiers 31 and 32 are different by adjusting the outputs of the drive power supplies 35 and 36. You can also make compensation possible.

  Other components can be configured in the same manner as the first entangled photon pair generating device 10, and thus redundant description is omitted.

  In this example, an optical bandpass filter 64 and an optical delay circuit 66 are provided in the third optical path 62 that connects the first optical amplifier 31 and the second optical amplifier 32. The optical bandpass filter 64 and the optical delay circuit 66 may be provided symmetrically including the optical bandpass filter and the optical delay circuit by providing the first optical path 60 and the second optical path 62, respectively. good.

(Second modification of first entangled photon pair generating device)
A second modification of the first entangled photon pair generating device will be described with reference to FIG. FIG. 5 is a schematic view of the entangled photon pair generating device 12 of the second modified example.

  Depending on the application, it may be necessary to form entangled photon pairs in the form of light pulses. Therefore, in the second modification, an optical modulator 68 is provided in the laser resonator 22. By this optical modulator 68, the excitation photons are converted into an optical pulse, and as a result, the entangled photon pair can be formed into an optical pulse. Moreover, since the peak intensity of the excitation photon increases, the efficiency is improved.

  Since components other than the optical modulator can be configured in the same manner as the first modification of the first entangled photon pair generating device, redundant description is omitted.

  In addition, although the structure which provides an optical modulator in the 1st modification of a 1st entangled photon pair generation apparatus was demonstrated here, you may provide an optical modulator in the 1st entangled photon pair generation apparatus.

(Second entangled photon pair generator)
With reference to FIG. 6, a second embodiment (hereinafter also referred to as a second entangled photon pair generating device) of a entangled photon pair generating device according to the present invention will be described. FIG. 6 is a schematic configuration diagram of a second entangled photon pair generating device.

  In the second entangled photon pair generation device 14, the nonlinear optical medium 41 has a signal photon and idler photon as a natural parametric down-converted light due to the cascaded second-order nonlinear optical effect on the excitation photon, or as a natural four-wave mixed light of the excitation photon. Is different from the first entangled photon pair generator.

  At this time, the optical frequencies ωp, ωs, and ωi of the excitation photons, signal photons, and idler photons satisfy the relational expression 2ωp = ωs + ωi. Further, the optical wavelengths λp, λs, and λi of the excitation photon, the signal photon, and the idler photon satisfy the relational expression 2 / λp = 1 / λs + 1 / λi. When a 1.5 μm band is desired as the wavelength band of the entangled photon pair, 1.5 μm may be used as the wavelength band of the excitation photon.

  In this case, the first and second photon pair extraction units are configured by a wavelength separation filter that extracts the signal photon and the idler photon from the laser resonator 24 and propagates the excitation photon into the laser resonator to generate laser oscillation. The For example, the wavelength separation filter can be composed of first and second dielectric multilayer optical filters 52 and 53.

  With reference to FIG. 7, the input / output characteristics of the wavelength separation filter will be described. FIG. 7 is a schematic diagram showing input / output characteristics of the wavelength separation filter. In FIG. 7, the horizontal axis indicates the optical frequency, and the vertical axis indicates the transmittance in arbitrary units. In FIG. 7, the solid line I indicates the transmittance output from the second input / output terminal with respect to the light input to the first input / output terminal, and the dotted line II is input to the first input / output terminal. The transmittance output from the third input / output terminal with respect to the measured light is shown.

  In this case, since the optical frequency transmitted through the first and second photon pair extraction units is limited to the optical frequency ωp of the excitation photon, a narrow band optical bandpass filter is not required.

  Since the other configuration can be configured in the same manner as the first entangled photon pair generating device, redundant description is omitted here. In addition, you may apply the 1st and 2nd photon pair extraction part with which a 2nd entangled photon pair generator is provided to a 1st entangled photon pair generator.

  In this second entangled photon pair generating device, the excitation photon, idler photon and signal photon are light in the same wavelength band. For this reason, it can comprise using the optical component which operate | moves in a single wavelength band, and the design of a coupling optical system becomes easy. Furthermore, inexpensive and highly reliable general-purpose parts can be used, and there is an advantage that reliability is improved and costs are reduced.

(Modification of second entangled photon pair generator)
A modification of the second entangled photon pair generating device will be described with reference to FIG. FIG. 8 is a schematic view of a modified example of the second entangled photon pair generating device.

  The entangled photon pair generating device 15 of this modification is different in the first and second photon pair extraction units, and the other configuration is the same as that of the second entangled photon pair generating device described with reference to FIG. Description is omitted.

  In this modification, the first wavelength separation filter includes a first optical circulator 54 and a first fiber Bragg grating (FBG) 56, and the second wavelength separation filter includes the second optical circulator 55 and the first optical circulator 55. 2 fiber Bragg grating (FBG) 57.

  The first optical circulator 54 includes first to third input / output ends 54a to 54c. The light input to the first input / output terminal 54a is output from the second input / output terminal 54b, the light input to the second input / output terminal 54b is output from the third input / output terminal 54c, The light input to the third input / output terminal 54c is output from the first input / output terminal 54a.

  The second input / output end 54 b of the first optical circulator 54 is connected to one end face 41 a of the nonlinear optical medium 41. The first input / output end 54 a of the first optical circulator 54 is connected to one end face 30 a of the optical amplifier 30. The third input / output terminal 54 c of the first optical circulator 54 is connected to the polarization plane converter 82 via the first FBG 56.

  The second optical circulator 55 includes first to third input / output ends 55a to 55c. The second input / output end 55 b of the second optical circulator 55 is connected to the other end face 41 b of the nonlinear optical medium 41. The first input / output end 55 a of the second optical circulator 55 is connected to the other end face 30 b of the optical amplifier 30 via the optical delay circuit 66. The third input / output terminal 55 c of the second optical circulator 55 is connected to the polarization beam splitter 84 via the second FBG 57.

  In the first and second FBGs 56 and 57, the wavelength λp corresponding to the optical frequency ωp of the excitation photon is a Bragg wavelength, and reflects the excitation photon of the optical frequency ωp. Light of other optical frequencies passes through the FBG.

  The excitation photons output from one end face 30 a of the optical amplifier 30 are input to the first input / output end 54 a of the first optical circulator 54. The light input to the first input / output end 54 a is output from the second input / output end 54 b and input to one end face 41 a of the nonlinear optical medium 41. The signal photons and idler photons generated by the nonlinear optical medium 41 are output from the other end face 41 b of the nonlinear optical medium 41 and input to the second input / output end 55 b of the second optical circulator 55. The light input to the second input / output terminal 55 b is output from the third input / output terminal 55 c and input to the second FBG 57. The second FBG 57 is configured to reflect excitation photons. The signal photons and idler photons pass through the second FBG 57 and are sent to the polarization beam splitter 84. On the other hand, the excitation photon output from the other end face 41b of the nonlinear optical medium 41 is reflected by the second FBG 57, and passes through the third input / output end 55c and the first input / output end 55a of the second optical circulator 55. Then, it is sent to the optical amplifier 30.

  The excitation photons output from the other end face 30 b of the optical amplifier 30 are input to the first input / output end 55 a of the second optical circulator 55. The light input to the first input / output end 55a is output from the second input / output end 55b and input to the other end face 41b of the nonlinear optical medium 41. The signal photons and idler photons generated by the nonlinear optical medium 41 are output from one end face 41 a of the nonlinear optical medium 41 and input to the second input / output end 54 b of the first optical circulator 54. The light input to the second input / output terminal 54 b is output from the third input / output terminal 54 c and input to the first FBG 56. The first FBG 56 is configured to reflect excitation photons. The signal photon and idler photon pass through the first FBG 56, pass through the polarization plane converter 82, and are sent to the polarization beam splitter 84. On the other hand, the excitation photon output from one end face 41a of the nonlinear optical medium 41 is reflected by the first FBG 56, and passes through the third input / output end 54c and the first input / output end 54a of the first optical circulator 54. Then, it is sent to the optical amplifier 30.

(Other embodiments)
In each of the above-described embodiments and modifications, an example in which the laser resonator is a loop resonator has been described, but the present invention is not limited to this. For example, the laser resonator may be a Fabry-Perot resonator.

  A case where the laser resonator is a Fabry-Perot resonator will be described with reference to FIG. 9A to 9C are schematic diagrams in the case where the laser resonator is a Fabry-Perot resonator. When using a Fabry-Perot type resonator, from the viewpoint of symmetry, a pair of optical amplifiers 31 and 32 are provided at positions sandwiching a nonlinear optical medium (see FIG. 9B), or an optical amplifier is sandwiched. A pair of nonlinear optical media 42 and 43 may be provided at the position (see FIG. 9C).

  In the case of a Fabry-Perot resonator, the reflecting mirror 70 is required. On the other hand, the loop resonator does not need to be provided with a reflecting mirror and is easy to be miniaturized. Therefore, it is more preferable to use a loop resonator.

10, 11, 12, 14, 15 Tangled photon pair generator
20, 21, 22, 24, 25 Laser resonator
30, 31, 32 Optical amplifier 34, 35, 36 Drive power supply 40, 41, 42, 43 Nonlinear optical medium
50, 51 Wavelength separation filter
52, 53 Dielectric multilayer optical filter 54, 55 Optical circulator 56, 57 Fiber Bragg grating (FBG)
60, 61, 62 Optical path 64 Optical band pass filter 66 Optical delay circuit 68 Optical modulator 70 Reflector 80 Photon pair output unit 82 Polarization plane converter 84 Polarizing beam splitter 86 Optical low pass filter 88 WDM filter

Claims (12)

An optical amplifier having optical gain in a frequency band including the optical frequency ωp and generating pumping photons of the optical frequency ωp;
Due to the nonlinear optical effect, a nonlinear optical medium that generates a photon pair of a signal photon of optical frequency ωs and an idler photon of optical frequency ωi from the excitation photon, and a position sandwiching the nonlinear optical medium in the propagation direction of the excitation photon A laser resonator including first and second photon pair extraction units for extracting the signal photon and idler photon, and lasing at an optical frequency ωp;
A polarization plane converter that rotates the polarization direction of the signal photon and idler photon extracted from the first photon pair extraction unit by 90 degrees;
A polarization beam splitter that combines the output light from the polarization plane converter and the output light from the second photon pair extraction unit;
A WDM (Wavelength Division Multiplexer / Demultiplexer) filter that spatially separates the output light from the polarization beam splitter into a wavelength component of the signal photon and a wavelength component of the idler photon ;
The optical amplifier is composed of a first optical amplifier and a second optical amplifier,
Said first and second optical amplifiers, said first and second photon pair extraction section, as well as quantum entanglement said nonlinear optical medium, characterized that you have been placed symmetrically around the non-linear optical medium Photon pair generator. 2. The quantum entangled photon pair generation device according to claim 1, wherein the laser resonator is a loop resonator. 3. The quantum entangled photon pair generation device according to claim 1, wherein an optical delay circuit is provided in the laser resonator. The quantum entangled photon pair generation device according to any one of claims 1 to 3, further comprising an optical modulator in the laser resonator. Between the polarizing beam splitter and the WDM filter,
An optical low-pass filter that transmits the signal photon and the idler photon and blocks a photon having an optical frequency given by the sum of the optical frequency ωs of the signal photon and the optical frequency ωi of the idler photon is provided. Item 5. The quantum entangled photon pair generation device according to any one of Items 1 to 4 . Said nonlinear optical medium, as a natural parametric down-conversion light to the excitation photons, entangled photon pairs generated according to any one of claims 1 to 5, characterized in that to generate the signal photon and the idler photon apparatus. Said nonlinear optical medium, as a natural parametric down-conversion light by cascade second-order nonlinear optical effect for the excitation photons, in any one of claims 1 to 5, characterized in that to generate the signal photon and the idler photon The entangled photon pair generator described. Said nonlinear optical medium, a natural four-wave mixed light of the excitation photons, entangled photon pairs generated according to any one of claims 1 to 5, characterized in that to generate the signal photon and the idler photon apparatus. In the laser resonator, comprising an optical bandpass filter that transmits the wavelength component of the excitation photons,
A low frequency component in which the first and second photon pair extraction units have a frequency less than a boundary frequency ωx between the optical frequency ωs of the signal photon and the optical frequency ωi of the idler photon and the optical frequency ωp of the excitation photon. of photons taken out of the laser resonator, according to claim 6, characterized in that it is composed of photons of the high frequency components at a wavelength separation filter that propagates in the laser resonator having the boundary frequency ωx or more frequencies Quantum entangled photon pair generator. The first and second photon pair extraction units extract the wavelength component of the signal photon and the wavelength component of the idler photon out of the laser resonator, and propagate the wavelength component of the excitation photon through the laser resonator. The quantum entangled photon pair generation device according to any one of claims 1 to 8 , wherein the quantum entangled photon pair generation device is configured by a wavelength separation filter. 11. The entangled photon pair generating apparatus according to claim 10 , wherein the wavelength separation filter is formed of a dielectric multilayer optical filter. The quantum entangled photon pair generation device according to claim 10 , wherein the wavelength separation filter includes a fiber Bragg grating and an optical circulator.

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